1. Field of the Invention
The present invention relates to bimetal snap-action type temperature control devices and more particularly, to a thermostat device, which has multiple manually resettable thermostat units arranged in a stack for working individually at different temperature ranges, and which allows a user to reset all the manually resettable thermostats at a time through one single action.
2. Description of the Related Art
According to the design of a conventional manually resettable bimetal snap-action thermostat, the bimetal snap-action spring plate is caused to curve from a first position to a second position when the temperature rises over a predetermined temperature. When the temperature drops below the predetermined temperature, the bimetal snap-action spring plate returns from the second position to the first position. At this time, the switch circuit is not reset, and an external force must be applied to reset the thermostat. This type of manually resettable thermostat has the advantages of high reliability and ease of use. Therefore, this type of manually resettable thermostat is intensively used in different fields. However, this type of manually resettable thermostat is workable only at one single temperature point. For multiple temperature control point application, multiple manually resettable thermostats shall be used. In case there is no sufficient installation space for multiple manually resettable thermostats, the aforesaid conventional design becomes useless.
For example, when designing an automatic rice cooker, as shown in FIG. 5, it is necessary to rapidly increase the heating temperature to a first temperature point t1, i.e., the food safety temperature about 60˜75° C. to kill microbes in rice, and then to lower the heating power for enabling the heating temperature to be increased slowly to a second temperature point t2, i.e., the saturation temperature about 85˜95° C. to have rice be well cooked, and then to lower the heating temperature to a third temperature point t3, i.e., the warm-keeping temperature about 60˜65° C. It is the most economic and convenient way to detect the first temperature point t1 and the second temperature point t2 by means of the use of a snap-action type thermostat. However, when the temperature drops, the snap-action type thermostat does not return to its former position automatically, i.e., it cannot let the heating temperature drop to the warm-keeping temperature point t3 to keep the cooked rice warm. This warm-keeping temperature point t3 is lower than the saturation temperature point t2. For the control of the first temperature point t1 and the second temperature point t2, a manually resettable thermostat can be used. The best installation position for thermostat between the electric heater and the cooker is the center area. However, the available space around this center area is limited. In a rice cooker, this space is sufficient for accommodating one single manually resettable thermostat. When multiple manually resettable thermostats are arranged together, the resetting mechanism will be complicated.